Filtration devices are known, e.g., from U.S. Pat. No. 1,475,572, DE-GM No. 75 11 229, DE-GM No. 80 19 310, and DE-OS No. 28 25 411. The removable casing upper part usually forms the inlet side in this structure, while the casing base part, usually provided with support legs, forms the outlet side. The base part of the filter support is accordingly formed by a grid, wire netting, or a perforated plate which forms the permeate chamber leading into the outlet. According to U.S. Pat. No. 3,031,082, the casing upper part is at its inside provided with support ribs which support the flat filter plate cut to size to prevent against a possible backwash from the outlet side. Such a support by ribs is sufficient when pressures from the backwash are low, or it may be entirely unnecessary when no backwash at all occurs. When high pressures occur, at the inlet side as well as from possible back wash, in more recent filtration devices (DE-GN No. 80 19 310) the casing upper part as well as base part are provided with the same filter support, so that damages to the membrane or flat filter plate cut to size on the basis of mechanical stress are impossible. The filter support in such devices consists usually of a perforated metal sheet which enters into a direct contact with the flat filter plate cut to size, and of a perforated metal sheet reinforcement arranged on the side of the perforated sheet facing away from the membrane, which reinforcement together with its hollow spaces forms the inlet-side or outlet-side fluid chamber. In the known devices, the entire filter support is positioned in a gradual recess of the casing parts. The handling of the casing upper part in such a structure is especially unsatisfactory since the filter support, after the placing of the flat filter plate cut to size upon the casing base part, must be held in place manually until the casing upper part is applied to the casing base part so as to cover it and with the aid of the tightening means the connection of the two casing parts can be established. Due to the need for handling, there is also the disadvantage that in the sterile filtration device the casing parts emerging from the autoclave, especially the upper part, might become non-sterile again unless the utmost care is applied in the feeding and in the construction.
To be sure, it is known (DE-OS No. 26 45 111) to support a backwash sieve arranged in the casing upper part by means of an elastic O-ring which rests in an outer closing edge of the backwash sieve and engages at various places protruding projections on the inside edge of the cover part in a detachable manner. This construction is, however, very expensive and is separate from the casing seal.
A further disadvantage of the known filtration devices consists in that the edge sealing is carried out by means of rotary O-ring seals arranged in at least one casing part, e.g., of silicone rubber, which after repeated autoclaving becomes brittle and shrinks, thus producing the danger of leaks.